1. Field of the Invention
The present invention relates to a planar antenna and, more particularly, to a small planar antenna combined with a printed circuit board.
2. Description of the Related Art
Antennas are classified into linearly (vertical or horizontal) polarized wave antennas, and circularly polarized wave antennas according to the polarization properties of incident electromagnetic waves. The linearly polarized wave is transmitted along a plane and thus it can be lost. In contrast, the circularly polarized wave is transmitted through two planes of the same size that cross each other, and interference from other devices can be eliminated because the circular polarization antenna is able to transmit two polarized components, the horizontally and vertically polarized waves. Thus, even if the position and direction of a transmission antenna or reception antenna changes, both transmission and reception of waves are possible, and there is an advantage of omnidirectional sensitivity.
Recently, the advance in wireless data communications has increased the need for the bluetooth PICO Net (BPN) antenna which couples personal computers (PCs), notebook PCs, printers, or mobile phones through a wireless network. The BPN antenna is a circular polarization antenna which has a consistent transmission/reception sensitivity in every direction, with non-directional properties, or an antenna capable of radiating a plurality of polarized waves.
On the other hand, a conventional circular polarization antenna includes an x-directional antenna arranged in the x-direction and an x-directional antenna which is arranged perpendicular to the x-directional antenna. Both the x-directional antenna and the y-directional antenna are half wavelength dipole antennas. Referring to FIG. 1, the wavelength of an x-directional horizontally polarized wave 1 radiated from the x-directional antenna has a phase difference of 90.degree. with respect to the wavelength of a y-directional vertically polarized wave 2 radiated from the y-directional antenna. Thus, circularly polarized waves can be obtained by powering the x-directional antenna and the y-directional antenna in sequence. However, a drawback of the conventional circular polarization antenna lies in that to provide the x- and y-directional antennas with the phase difference of 90.degree., a phase shifter for delaying a radio frequency (RF) signal fed from an RF signal module of the antenna is needed. In addition, the complicated structure of the antenna hinders production of a small antenna.